50 HETEROSTYLED DIMORPHIC PLANTS. CHAP. I. 



be added, according to Axell, P. stricta. Mr. Scott ex- 

 perimented on P. Scotica, mollis, and verticillata, and 

 found that their flowers yielded an abundance of seeds 

 when fertilised with their own pollen. This shows 

 that they are not heterostyled in function. P. Scotica 

 is, however, only moderately fertile when insects are 

 excluded, but this depends merely on the coherent 

 pollen not readily falling on the stigma without their 

 aid. Mr. Scott also found that the capsules of P. 

 verticillata contained rather more seed when the flowers 

 were fertilised with pollen from a distinct plant than 

 when with their own pollen; and from this fact he in- 

 fers that they are sub-heterostyled in function, though 

 not in structure. But there is no evidence that two 

 sets of individuals exist, which differ slightly in func- 

 tion and are adapted for reciprocal fertilisation; and 

 this is the essence of heterostylism. The mere fact 

 of a plant being more fertile with pollen from a dis- 

 tinct individual than with its own pollen, is common 

 to very many species, as I have shown in my work " On 

 the Effects of Cross and Self-fertilisation." 



HOTTONIA PALUSTRIS. 



This aquatic member of the Primulaceae is con- 

 spicuously heterostyled, as the pistil of the long-styled 

 form projects far out of the flower, the stamens being 

 enclosed within the tube; whilst the stamens of the 

 short-styled flower project far forwards, the pistil being 

 enclosed. This difference between the two forms has 

 attracted the attention of various botanists, and that 

 of Sprengel,* in 1793, who, with his usual sagacity, 

 adds that he does not believe the existence of the two 

 forms to be accidental, though he cannot explain their 



* 'Das entdecke Geheiinniss der Natur,' p. 103. 



